A. Field of the Disclosure
The present disclosure relates generally to mapping systems and methods for mapping anatomic structures, and more particularly to such mapping systems and methods which use a non-contact catheter.
B. Background Art
Cardiac tachyarrhythmia is often caused by conduction defects which interfere with the normal propagation of electrical signals in a patient's heart. These arrhythmias may be treated electrically, pharmacologically or surgically. The optimal therapeutic approach to treat a particular tachyarrhythmia depends upon the nature and location of the underlying conduction defect. For this reason electrophysiologic (EP) mapping is commonly used to explore the electrical activity of the heart during a tachyarrhythmic episode. The typical electrophysiologic mapping procedure involves positioning an electrode system within the heart. Electrical measurements are made which reveal the electrical propagation of activity in the heart. If ablation is the indicated therapy, then a therapy catheter is positioned at the desired location within the heart and energy is delivered to the therapy catheter to ablate the tissue.
Three-dimensional mapping techniques typically include either contact mapping or non-contact mapping. In contact mapping, one or more catheters including one or more electrodes are advanced into the heart. Electrophysiological signals resulting from the electrical activity of the heart are obtained by the one or more electrodes with at least the catheter and in some methods the electrodes in contact with the endocardial surface of the heart—e.g., a particular heart chamber. Multiple data points are obtained on the internal surface of the heart and are used to construct a three-dimensional depiction of the heart.
For non-contact mapping, one or more catheters carrying one or more electrodes are located within the heart in spaced proximity to the endocardial surface of the heart. Signals are detected by the electrodes and used to correlate the spatial positions of the electrodes relative to a previously determined three-dimensional model of the heart (or portion of the heart being mapped). Conventional modeling systems exist for generating such a three-dimensional model of the heart utilizing technology such as CT scan, MRI, radar imaging, x-ray imaging, and fluoroscopic imaging. Such data is often processed using a three-dimensional modeling technique—commonly some form of a Boundary Element Method (BEM) such as a spline BEM or linear BEM. The imaging process is performed hours and in some cases days in advance of the treatment and/or surgery.
The system must determine, using the signals detected by the electrodes, the relative position of each of the electrodes and then correlate such data with the previously generated three-dimensional model. Due to any number of factors associated with such a mapping technique, such as the actual distance of the electrodes away from the endocardial surface, the movement of the endocardial surface as signals are being detected by the electrodes, etc., the determined relative electrode positions may be exterior to the boundary surface of the three-dimensional model. Prior non-contact mapping systems, and in particular the inverse problem of electrocardiography and the underlying equations of the BEM in such systems, make the assumption that the electrodes are contained with the boundary surface of the three-dimensional model. It has occurred, though, that erroneous and perplexing reconstructions of the heart electrophysiology can result from such assumptions when the relative positions of the electrodes indeed lie exterior to the boundary surface of the three-dimensional model.
It is thus desirable for a mapping system (and more particularly a non-contact mapping system) and method that is used for mapping an anatomic structure to not assume all relative positions of the measurement electrodes lie within the boundary surface of a three-dimensional model of the anatomic structure. It is further desirable that such a mapping system and method can make adjustments to account for situations in which the relative positions of one or more measurement electrodes lie exterior to the boundary surface of the three-dimensional model of the anatomic structure.